Barbed wire fences or entanglements consisting of one or more extended rolls of barbed wire have long been used in theatres of war as obstacles to infiltration or attack by opposing forces.
Whereas furtive incursion may sometimes be accomplished by cutting strands, one by one, with hand operated wire cutters, such a method exposes the infiltrators to extreme danger if their activity is noticed by the enemy. For this reason, when it has been considered necessary for a body of men to traverse a fence rapidly, manual severing of the fence is typically replaced in favour of using explosives.
Since the First World War, the preferred type of explosive charge to breach wire obstacles with advantageous rapidity has been a device known as “Bangalore Torpedo” used both as a factory-filled item and in improvised versions. The Bangalore Torpedo consists of a thin-walled, cylindrical, metal tube, or arrays of such tubes joined end to end, filled with explosive. Most commonly such tubes are steel and they are filled with a mixture of ammonium nitrate and TNT (amatol) or with TNT alone; improvised versions have consisted of steel pipes filled with guncotton primers. These charges are thrust or thrown beneath, through or above the obstacle and, once the operator has retired to a safe distance, are detonated by means of safety fuse or electric detonators.
Individual factory-made charges, which are typically about 1.8 meters long, and of approximately 38 mm diameter, with a wall thickness of approximately 2 mm, and containing approximately 2 kgs of explosive in each unit, are provided with bayonet fittings or screw threads at their ends so that they can be quickly assembled into a linear array when this is necessary. One end of the charge, or the charge array, is provided with a pointed, rounded, or ogival nose in order to facilitate the sliding over possibly rough ground or the easy insertion into a wire entanglement without snagging.
The charge depends for its effectiveness upon the blast effect of the explosive it contains which both stretches adjacent strands of wire to the extent that they break and displaces them to either side, thereby forming a gap in the obstacle wide enough for one or more combatants to pass through. The effect is enhanced by the impact of fragments of the tubular case which are projected at high velocity in radial directions.
Such charges may also be used for the displacement or the destruction and consequent rendering safe of anti-personnel or anti-vehicle mines lying on the ground's surface or buried a short distance beneath and also as a tool for general demolition.
It will be understood by those skilled in the art that this type of explosive charge suffers several limitations. The first of these is that the length of the unit charge of the existing Bangalore Torpedo is such that it is awkward to carry and unnecessarily large to use as a means of severing, for example, just a few strands of wire or destroying a small object such as an unexploded projectile or electrical installation.
Another disadvantage derives from the fact that, as a consequence of scaling, in order to double the range at which blast from such a charge would sever a length of wire of a given strength situated to one side, the diameter of the charge would also need to be doubled. This would increase the explosive load four-fold. In practical terms this means that the ability of a charge of given size to sever wire diminishes rapidly with distance.
A further disadvantage of the device is the danger presented to the operator and his colleagues by the very sharp and jagged steel tube fragments of the bursting tube, this danger being exacerbated by the frequent need of an operator intending to breach an obstacle to be as close to the obstacle as possible in order to advance immediately afterwards.
One known way of greatly extending the effective range of charges of high explosive employs the principle of the shaped charge in which the advancing detonation wave front progressively collapses a metal-lined cavity provided in the outer border of the explosive. Collision of the consequently converging increments of the material lining the cavity has a mutually reinforcing effect on their mean velocity. Thus a generally cylindrical mass of explosive, initiated on the long axis at one end and having a metal-lined conical cavity with an apex angle typically between 40° and 100° at the other, squeezes the liner into a “jet”, consisting of narrow wire of extremely high velocity with a considerable velocity gradient along its length, the tip travelling much faster than the rear end. Such jets have great penetrating power, but the velocity gradient causes them to break up in flight and the effective range is therefore usually limited to a distance equivalent to a few charge diameters.
If, however, such a charge is provided not with a metal-lined conical cavity but with a shallow indentation, which may be conical but is more commonly approximately spherical or hyperbolic, then the liner material is squeezed along the long axis of the charge but no jet is formed. The consolidated material is projected at a lower velocity than a corresponding jet but, since it is less elongate, it travels as a coherent mass, undergoes much less disintegration and consequently has a very much greater effective range. The projectiles generated by such charges are generally known as “explosively formed projectiles” or EFPs.
This principle of a collapsing metal lined cavity can also be applied to elongate, or linear, shaped charges in which case the cavity consists of a groove running the length of the elongate mass of explosive. Such liners are usually angular in transverse section but cylindrical grooves are also effective. Such charges are most commonly used for making long cuts in flat, circular or undulate steel targets.
Much less frequently used are linear charges with such shallow lined grooves as produce linear EFPs. These produce elongate, rod-like, projectiles which, though less penetrating at close range than linear cutting charges, are capable of producing a practical effect at ranges much greater than those at which linear cutting charges produce useful effects. The shape of the projectiles depends upon the cross-sections of the liner and of the explosive charge.
In order to make wire fences and entanglements more resistant to cutting by whatsoever means, during recent decades types of wire have been introduced which are harder and stronger and thus more resistant to cutting and snapping.
Objects of the Invention
An object of the present invention is to overcome these disadvantages.